Significant improvements in both fuel efficiency and performance of an internal combustion engine may be realized by selective switching of a cam profile. However, cam profile switching technologies have been difficult to implement in various valvetrain settings, such as roller finger follower valvetrains.
One method of implementing cam profile switching in a roller finger follower valvetrain has been to utilize a “drop finger” follower, wherein the roller finger is movably coupled to the follower body in such a manner that the finger can be operated in either a coupled mode, in which the roller finger is locked in position relative to the follower body, or in a decoupled mode, in which the roller finger is decoupled from and allowed to move relative to the follower body. This allows the cam and valve to have different lifts, depending upon whether the roller finger is coupled to or decoupled from the follower body.
One difficulty that has been encountered in implementing roller finger follower valve systems involves actuation of the roller finger decoupling mechanism. Both hydraulic and electromechanical actuation systems have been proposed. However, hydraulic systems may cause a power demand on the engine, as these systems require the oil pump to do additional work. Likewise, solenoids used in electromechanical systems may be relatively large and bulky.
The inventors herein have realized that the above-described problems may be addressed through the use of a mode-switching cam follower having a body, a cam contact movably coupled to the body, a latch member movably coupled to the body, wherein the latch member is movable between a coupled position in which the cam contact is held in a fixed relation to the body by the latch member and a decoupled position in which the cam contact is decoupled from the latch member and movable relative to the body, and an actuator in communication with the latch member, wherein the actuator comprises a shape memory alloy member. In some embodiments, the cam contact includes a roller finger, while in other embodiments includes a sliding contact. Such a mode-switching cam follower may allow actuation of the latch member while avoiding problems with the size and power demands found in other actuation systems.